What's a company to do when that image-maker tarnishes?

Or so says tennis star Andre Agassi in a commercial he did for Canon products. Certainly, it's a slogan he believes.

Rebellious and sometimes outrageous, Mr. Agassi is as well-known for the hair on his chest (and back) as he is for his

backhand. He wears ponytails. He dates movie stars. He wears purple shirts in a sport where the traditional uniform is white. It's an anti-establishment image that gives him fan adulation and media attention.

It's an image Canon wanted when they hired him as their spokesman.

A look. An attitude. An act. That's what companies want when they hire celebrities to hawk their products. Whether it's "Murphy Brown's" Candice Bergen talking a mile a minute in the Sprint ads or Michael Jordan flying through the air and dunking basketballs in Nike commercials, most celebrities stick to their public image when doing endorsements. That is, after all, why they are hired.

But what if that image changes?

The child-abuse allegations against pop star Michael Jackson, the messy divorce between Burt Reynolds and Loni Anderson, the gambling rumors surrounding Michael Jordan -- all these show just how vulnerable companies are to the images of the celebrities who endorse their products.

Companies justify this expense because they believe having a celebrity touting their products means an increase in visibility and, eventually, an increase in sales. They hope to cash in on the images that these celebrities have established -- Mr. Jackson's childlike behavior, Mr. Jordan's feats on the basketball court, Ms. Crawford's beauty, Ms. Bergen's wit and sophistication. The marriage between celebrities and endorsements has made both sides millions.

Now that marriage is rocky, and some in the industry are wondering if these companies are relying too much on these public personas.

Mr. Jackson, Mr. Jordan and Mr. Reynolds have all had their images tainted in recent months. Mr. Jackson's troubles are possibly the most damaging. Last week, media reports disclosed that a 13-year-old boy has told Los Angeles Children Services and police that Mr. Jackson sexually molested him. Mr. Jackson's representatives deny the allegations and say the accusations stem from a failed $20 million extortion attempt.

PepsiCo and Sony Inc., two of the sponsors of Mr. Jackson's current "Dangerous" tour, are both taking a wait-and-see approach.

Some analysts say Mr. Jackson's image -- and his relationship with his sponsors -- has been damaged no matter what the outcome of the allegations.

"I don't think we'll see a big public break between Pepsi and Jackson," says Marcy Margiera, a senior reporter for Advertising Age who covers the beverage and entertainment industries. "I think they'll just quietly let his contract run out. It ends in December, so they will be OK."

Others say getting the right celebrity to pitch your product is worth the risk. And good publicity.

"I think there are a lot of companies out there who would love to have Sharon Stone as their spokesperson," says Alison Lazar, director of new business development for Celebrity Endorsement Network in Los Angeles. Celebrity Endorsement Network hires talent on behalf of advertisers. "And she's as controversial as they come."

Ms. Lazar admits many companies would think twice about hiring Ms. Stone. "But someone could come up with a clever marketing campaign and play up her controversial stature. Kind of poke fun at it."

In the early days of television, celebrities endorsed everything from dishwashing soap to washing machines. Some of the most popular ads were for cigarettes and alcohol. The celebrities simply held up a product, looked into the camera and essentially said, "Buy this, it works."

Times have changed. Celebrities rarely plug booze, cigarettes or even fur (not good for their image), but tout everything from adult diapers to Nuprin. Holding a product and looking into a camera isn't enough in today's MTV world. Celebrities not only sell a product, but an image. Buy this and you can be like me (or Mike) is the message.

"Unfortunately, hiring a celebrity to sell your product has become a standard marketing tool," says Michael Jacobson, co-founder of the Center for the Study of Commercialism, a nonprofit group based in Washington, D.C. "Companies care more about an image than about the quality of their product.